Re: [PATCH] check_refname_component: Optimize
From: Junio C Hamano <hidden>
Date: 2016-06-15 23:01:25
David Turner [off-list ref] writes:
In a repository with tens of thousands of refs, the command ~/git/git-diff-index --cached --quiet --ignore-submodules [revision] is a bit slow. check_refname_component is a major contributor to the runtime. Provide two optimized versions of this function: one for machines with SSE4.2, and one for machines without. The speedup for this command on one particular repo (with about 60k refs) is about 12% for the SSE version and 8% for the non-SSE version. Signed-off-by: David Turner <redacted>
Just a few quick impressions (I do not have time today to look at new patches). - The title seems a bit strange. Perhaps "refs.c: optimize check_refname_component()" or something? - "~/git/git-diff-index" looks doubly strange in that the issue you are addressing would not depend on your compiled Git being installed in your $HOME/git at all. For that matter, from the command line and the patch, I am not sure if this is specific to "git diff-index", or the same issue exists for anything that takes revs and pathspecs from the command line.
quoted hunk
--- Makefile | 6 +++ configure.ac | 6 +++ refs.c | 143 +++++++++++++++++++++++++++++++++++++++++++++++++++-- t/t5511-refspec.sh | 13 +++++ 4 files changed, 163 insertions(+), 5 deletions(-)diff --git a/Makefile b/Makefile index a53f3a8..123e2fc 100644 --- a/Makefile +++ b/Makefile@@ -1326,6 +1326,11 @@ else COMPAT_OBJS += compat/win32mmap.o endif endif +ifdef NO_SSE + BASIC_CFLAGS += -DNO_SSE +else + BASIC_CFLAGS += -msse4 +endif ifdef OBJECT_CREATION_USES_RENAMES COMPAT_CFLAGS += -DOBJECT_CREATION_MODE=1 endif@@ -2199,6 +2204,7 @@ GIT-BUILD-OPTIONS: FORCE @echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@ @echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@ @echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@ + @echo NO_SSE=\''$(subst ','\'',$(subst ','\'',$(NO_SSE)))'\' >>$@ ifdef TEST_OUTPUT_DIRECTORY @echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@ endifdiff --git a/configure.ac b/configure.ac index b711254..71a9429 100644 --- a/configure.ac +++ b/configure.ac@@ -382,6 +382,11 @@ AS_HELP_STRING([],[Tcl/Tk interpreter will be found in a system.]), GIT_PARSE_WITH(tcltk)) # +# Declare the with-sse/without-sse options. +AC_ARG_WITH(sse, +AS_HELP_STRING([--with-sse],[use SSE instructions (default is YES)]), +GIT_PARSE_WITH(sse)) + ## Checks for programs. AC_MSG_NOTICE([CHECKS for programs])@@ -449,6 +454,7 @@ else fi fi GIT_CONF_SUBST([TCLTK_PATH]) +GIT_CONF_SUBST([NO_SSE]) AC_CHECK_PROGS(ASCIIDOC, [asciidoc]) if test -n "$ASCIIDOC"; then AC_MSG_CHECKING([for asciidoc version])diff --git a/refs.c b/refs.c index 28d5eca..8ca124c 100644 --- a/refs.c +++ b/refs.c@@ -5,6 +5,8 @@ #include "dir.h" #include "string-list.h" +#include <nmmintrin.h> +
We would prefer not to add inclusion of any system header files in random *.c files, as there often are system dependencies (order of inclusion, definition of feature macros, etc.) we would rather want to encapsulate in one place, that is git-compat-util.h.
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/* * Make sure "ref" is something reasonable to have under ".git/refs/"; * We do not like it if:@@ -29,30 +31,160 @@ static inline int bad_ref_char(int ch) return 0; } +char refname_disposition[] = { + 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,... + 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 +}; +
Does this array need to be extern? Is this table designed to take both positive and negative values? If the answer is "I expect we add only positive", then please make it explicitly "unsigned char". What do these magic numbers in the array mean? How were the values derived? What are you doing in this commit to help others who later need to debug, fix and enhance this table?